Magneto-telephone



(No Model.)

S. D. FIELD.

MAGNET() TELEPHONE.

No. 575,394. Patented Jan. 19, 1897.

UNITED STATES PATENT OEEICE.

STEPHEN D. FIELD, OF STOCKBRIDGE, MASSACHUSETTS, ASSIGNOR TO THEAMERICAN BELL TELEPHONE COMPANY, OF BOSTON, MASSACHUSETTS.

IVIAGNETO-TELEPHONE.

SPECIFICATION forming' part of Letters Patent No. 575,394, dated January19, 1897'.

Application Bled August 11,1896. Serial No. 602,387. (No model.)

To tu whom t may concern:

Beit known that I, STEPHEN D. FIELD, residing at Stockbridge, in thecounty of Berkshire and State of Massachusetts, have in-v vented certainImprovements in Magneto- Telephoncs, of which the following is aspecification.-

This invention relates to magneto -telephones such as are most generallynow em- Io ployed as receivers. Its object is to produce areceiving-telephone which shall be capable of responding to the rapidchanges of voicecurrents more promptly than has heretofore been foundpossible, and one whose reprod uction of the transmitted sounds willtherefore be extremely accurate and faithful without involving anycounteracting loss in volume. An application for patent filed of evendate herewith for improvements in electromag- 2o netic apparatusdescribes electromagnetic appliances and receiving instruments dependingfor their normal operation upon the difference in time required byexciting-coils of like magnetizing power, but diverse induc- 2 5 tance,wound over or placed upon a common iron core, to reach, respectively,their maximum and zero magnetizing values under abrupt changes of acurrent traversing the said coils. The same underlying principles 3o areinvolved in the present invention, wherein the iron core or pole-pieceof the active pole of the telephone-magnet is associated with twocontrolling electromagnetic or exciting helices joined up between thebinding-screw terminals of the instrument in parallel cir-` cuit ormultiple arc with one another and adapted thereby to be connected inseparate parallel branchesot' the same working circuit. These twohelices are so constructed as lo pos- 40 sess equal magnetizing powerswhen submitted to the action of the same steady current; or, in otherwords,when such a current divides between them both have the same numberof ampere-turns. They are, however, likewise so relatively constructedand arranged that the inductance of one of them shall be much higherthan that of the other, and by this means any rapidly-varying current,such as atelephone-current, passing through the circuit and through thetwo coils in parallel reaches its maximum when rising or appearin g andits minimum when falling or disappearing with much greater celerity inthe low-in ductance helix than it can in the other. Moreover, the saidhelices are wound over or placed 5 5 upon their coreor connected up inopposition to each other, so that each tends to oppose the magnetizingeect of the other, and. when a current, having passed its variablestate, is steady or fully established through both, and 6o boththerefore exert their full magnetizing infiuence on the ironmagnet-core, each neutralizes the effect of the other on said core, andthe result is a zero of action. The spools or bobbins whereon the twohelices are wound 6 5 are preferably of the same or .substantially t-hesame mechanical dimensions; but the high-inductance helix is wound withfine insulated wire, while the wire of the low-inductance helix isrelatively large, so that while 7o the spool of the former requires tofill it a great number of convolutions that of the latter is iilled by amuch smaller number of turns. The appropriate size of spool having beenselected, the size of wire for both and the relative number of turns for both required to substantially lill the said spools and at the sametime to insure that the two shall be enabled to exercise a substantiallyequal magnetizing influence can readily be determined 8o by thewell-known rules of electrical engineering practice.

In the telephone an initial magnetization is, as usual, imparted to thesoft-iron core or pole-piece by a permanent or temporary magnet. When aworking-current impulse of given polarity or direction is transmittedthrough the main line, it circulates through both windings. In one-saythe low-inductance coil-it first passes round the core in a 9o directionto decrease or weaken the original polarity, while its direction roundthe core in the other is such as to tend to strengthen the initialpolarity; but since in the coil of low inductance the current reachesits normal value much quicker than it does in the other the polarity ofthe core is acted upon practically in the first place by that coilalone, and since, also, the main-line working current of a telephonesystem is either one of too most rapid alternation or, as in rareinstances, of rapid strength variation it becomes evident that the saidfirst impulse of current in the quick-acting c'oil is swiftly reversedor b'egins to change, and that such reversal or change is necessarilyassisted by the more sluggish action of the high-inductance coil, whichallows its portion of the iirst impulse of the current to reach itsnormal value and to act upon the core in opposition to that of the othercoil, but an instantlater. Thus the action on the core of each reversalor change of current in the quick helix of low inductance is facilitatedby the slower action upon the said core of the more sluggish coil, whichoperates as a kind of curb to shorten up and sharpen the said reversalsor changes,

enabling them to be fully accomplished much quicker than otherwise wouldbe the case.

I have attained good results with a differen tal-inductance telephone,in which I associated with the ordinary bar-magnet and diaphragm afork-shaped soft-iron core having a bridge of iron extending between thetwo pron-g ends of the fork, the whole forming a soft-ironp'arallelogram provided at its centei', which was located immediatelybehind the middle of the diaphragm, with a polar projection orpole-piece. In this instrument thev two coils surrounded, respectively,the two portions ot' the iron bridge between the said central pole andthe prong ends, and I prefer this or a similar arrangement.

The invention may, however, be readily embodied in atelephone ofstandard construction', to which is added the high-inductance helix inthe form of a flat coil surrounding the inner or l'ow-inductance helixand concentric with that and with an ordinary cylindrical core.

In the, drawings accompanying and illustrating this specification,Figure l represents a hand or receiving telephone broken away near theearpiece to show a preferred polepiecel construction and coilarrangement in which my invention may be embodied. Fig. 2' is adiagrammatic detail indicating more clearly the said form of pole-pieceand mode of winding the two electromagnetic helices. Fig. 3 is a frontView of the helices and polepiece, `the cap-piece and diaphragm beingremoved. Fig. 4 represents in elevation the arrangement of the workingparts of a modification; Vand Fig. 5 is a front View of the coils y andpolar end of the magnet thereof, the diaphragm being removed.

Hlitei'erring i'n the first place to Figs. l-, 2, and 3', T is ahand-telephone i-n which my invention is incorporated, C bein-g theusual 'cas'ethereon provided at one end with an expansion-chamber e forthe polepi-ece and coils and` at the other with bind-ing-screwtermin'alsB and B2, whereby the instrument and itsinte'rn'al connections may beunited through the external circuit and a transmitter.

'M is the usual permanent magnet, D the diaphragm, and E the cap or earpiece, which is screwed over the expansion-chamber and secures the edgeof the diaphragm. A forked pole-piece P, of soft iron, having two prongsff?, is attached to the magnet by a projecting piece at, which is boltedbetween the ends of the bars composing the magnet, and a bridge-piecel), also of soft iron, unites the prongs f and f2 magnetically, forminga softiron parallelogram. A central polar projection p extends outwardlyfrom the middle oi'I the bridge-piece to a point in close proximity tothe middle of the rear side of the diaphragm.

I is a magnetizing, exciting, or actuating helix made of many turns ofine magnetwire, placed on or'wound over the bridgepiece between thecentral pole p and one of the fork-prongs, (in this ins-tance the prongf,) and 1l is another actuating-helix formed of a much smaller number ofturns of a larger size of magnet-wire. By reason of thisy construction,regard-less of their relative resistance or magnetizing power, theinductance of the helix I is very much higher than that of the coil t',so that when both are being operated by the same rapidly-varying currentthat portion of the current which traverses the coil I is slower both inrising to its maximum or in falling to its minimum value than theport-ion which passes through the coil t, and it follows, of course,that the magnetizin g or dem'agnetizing action of I is much moresluggish than that of t' upc-n the central pole p, which is common toboth.

L and L2 are the conducting-wire`s,gconnect ing both hielices in circuitbetween tlre screwterminals B B2, and at any convenient point betweenthe bindingscrewsk and the coi-ls the said conductors divide into twoparallel branches, in which are respectively connected the helices I i.One branchis traceable bietween conductors L and L2 by way ofconnecting-wire 2, helix i, andwire 3, while the other may be tracedthrough wire 4, helix I, and Wire 5.

As indicated in Fig,y 2, the two windingsy are reversely connected, sothatA when a current impulse of given direction is sent through thecircuit and instrument the magnetic action' of each on the cen-traipol-e p tends to oppose that of the other. The magnetizing 'force of thehelices I and t' are equal, and as t' is the quicker in reaching itsmaximum and also its mini-mum value the influence upon the pole p of t'alone isv at first manifested, but is checked' and its following changemade moreV expeditious by the more-slowly-exercised opposing' influenceof I. Since thel same phenomenon occurs with every current variation,itis obvious that them-agnetic changes, which by their action on thediaphragm are transformed into` mechanical motion, are enabled to morefaithfully copy the form of the voice-currents developed ijn the circuitby the distan-t transmitter. Hence the reproduction of thetransmitter-'sounds is: ef-

fectuated with great accuracy.

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In the telephone to which I have hereinbe fore referred as having` beenmade by me the high-inductance helix I was made by employing such a sizeof wire that its spools was properly iilled when the resistance measuredthree hundred ohms, and the low-inductance coil t' was made by windingwith wire of such size that its spool s2 was filled when the measuredresistance was seventy five ohms. Roughly, therefore, it may be saidthat the magnetizing power of the coils is equal and their inductancessufiiciently dissimilar when with spools of the same size both filledwith wire the resistance of the winding of the high-inductance coil isfour times that of the low-inductance coil, which according to standardpractice may be seventy-five ohms or thereabout. More generally we mayconsider that under average conditions the two helices have suitablerelative proportions when the resistance of I is approximately fourtimes that of t' and when in both the product of the number of turnsinto the strength of the current circulating in the helix is the same.

In the modification illustrated by Figs. 4L and 5 the two helices areplaced concentric with one another, the high-inductance coil I occupyingthe outermost position and both encircling the soft-iron core p of thetelephonemagnet, the said core and the lowinductance coili being ofordinary dimensions and form. In this modification, IWI is the magnet;p, its soft-iron pole-piece or core; t', an actuating helix immediatelysurrounding the said core and connected in a branch 2 3 of the circuit LL2; I, asecond helix of much higherinducg tance than the former placedso as to surround the said former helix and core and connected inparallel with the former in the branch 4 5 of the same working circuit LL2, and D is the diaphragm.

In Figs. 2 and 4 the arrows indicate that at any given moment thecurrents in the two coils have opposite magnetiziiig direction.

In the modification of Figs. 4 and 5 the inner coil may, as usual, havea resistance of seventy-five ohms,and may be formed of seven hundred andfifty convolutions, and in that case the coil I may have six thousandconvolutions and a resistance of six hundred ohms.

It is apparent that my invention is not rcstricted to either of theparticular forms of telephone herein specifically shown and den scribed,and that the spirit of the said invention would also lind embodiment ina form having its two coil-wires wound on the same spool or in anyanalogous arrangement, pro vided that the magnetizing forces of the saidtwo wires were alike, their inductances un like, and their winding orconnection reciprocally reversed with respect to their action on themagnet-core.

Having described my invention, I claiml. A magnetdtelephone comprisingincombination a diaphragm, a magnet7 a pole-piece therefor, as described,and two oppositely wound or connected magnetizing or exciting helices ofequal magnetizing power, but dissimilar inductance, associated with thesaid pole-piece, the said helices being in parallel or multiple arc withone another between. the instrument-terminals, and adapted thereby to beconnected in parallel in the same working circuit.

2. A differential-inductance magneto-telephone having its magnetpole-piece or core associated with two oppositely wound or connectedexciting or actuating coils connected in parallel with each other, oneof the said coils being formed of a relatively short .and coarse wire,and the other of a relatively long and line wire, and both having suchproportions that when the currentof the working circuit divides betweenthem, their ampereturns shall be the same 5 substantially as and for thepurposes specified.

3.l The combination in a magneto -telephone, of the magnetized soft-ironcore or pole-piece, with two independent electromagnetic helices ofequal and opposite magnetizing power but un equal inductance, surroundning the said core, in such manner as to excite opposite magnctizationstherein, under the iniiuence of the saidworkng current, and therebyfacilitate the required magnetic changes thereof, the said helices beingin separate parallel branches of the same circuit.

4f. In a magneto-telephone,the combination substantially as described,of the vibratory diaphragm and inducing-magnet, with a forked pole-piecefor the said magnet having an iron bridge-piece uniting its ends, andforming therewith a soft-iron parallelogram, having a central poleprojecting close to the diaphragm center, and two oppositely wound orconnected exciting or actuating helices in parallel circuit with eachother, surrounding the said bridge-piece one on each side of the centralpolar projection ;v the said helices being of similar magnetizing powerwhen submitted to the same steady current, but of dis similarinductance.

In testimony whereof I have signed my name to this specification, in thepresence of two subscribing witnesses, this 28th. day of July7 1890.

STEPHEN D. FIELD.

Witnesses:

THoMAs D. LocK'wooD, JOSEPH A. GATELY,

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